1. Field of the Invention
The invention relates both to novel, improved, nonhydrolyzable block copolymers of siloxanes and organic ethers, preferably, polyethers which are either branched or linear in structure and to novel methods for making the copolymers. The invention also relates to novel improved methods for making urethane foams using said novel improved copolymers as surfactants or foam stabilizers.
2. Description of the Prior Art
Certain types of nonhydrolyzable siloxane-polyether copolymers are well known and are readily available articles of commerce. The siloxane polyether copolymers contained in the above products are made by the co-reaction of poly(dimethyl-siloxanes) containing SiH groups (hydrosiloxanes) with olefinic polyethers wherein the olefinic sites are allyl groups. The general reaction whereby these nonhydrolyzable linkages are created between silicone and polyether groups is: ##STR1##
However, the above reaction is not the sole reaction which occurs during the preparation of the copolymer. It has been established that a significant percentage of the allyl groups are isomerized under the addition reaction conditions to propenyl groups. The latter react very slowly, if at all, with the SiH groups of the hydrosiloxane reactants: ##STR2## See, for example U.S. Pat. Nos. 3,507,923 and 3,836,560 (col. 10). It has become accepted practice within the industry to use stoichiometric excesses (20 mole % or more) of allyl polyethers to insure reactions of all the .tbd.SiH groups, or to scavenge the residual .tbd.SiH groups with a nonpolyether reactant such as methanol or ethylene. The excess unreacted or isomerized allyl polyether is thus present as diluent, reducing thereby the potency or active concentration of the final polymer.
In U.S. Pat. No. 3,507,923 the patentees disclose that the capping of methallyl alcohol started oxyalkylene polymers results in minimization of the undesirable formation of isobutenyl groups (CH.sub.3 --C(CH.sub.3).dbd.CH--) from the methallyl groups (CH.sub.2 .dbd.C(CH.sub.3)--CH.sub.2 --). However, there is no disclosure that the methallyl groups show a lower degree of isomerization than do allyl groups during hydrosilation. Based on the teachings of this patent, the skilled worker could expect that methallyl groups would behave in a manner similar to allyl groups under hydrosilation conditions.
Siloxane polyether copolymers containing --CH.sub.2 CH(CH.sub.3)CH.sub.2 -- linkages between siloxane and polyether groups have been prepared by the reaction of sodium polyether alkoxides and chloroisobutyl silicones (see U.S. Pat. No. 3,414,604 to E. J. Pepe and B. Kanner, Chem. Absts., 65, 17002c (1966)). A similar approach, using chloroisobutyl silicones and polyether carboxylate salts, had yielded copolymers with --CH.sub.2 CH(CH.sub.3)CH.sub.2 O.sub.2 CCH.sub.2 -- groups between silicone and polyether blocks (see Ger. Offen. No. 1,961,501, Chem. Absts., 73 78069f (1970)). Several Japanese patents disclose more typical nonhydrolyzable pendant copolymer preparations from polyhydrosiloxanes and allyl or methallyl methoxy polyalkylene glycols (see Jap. Kokai No. 74 40,398, Chem. Absts. 83, 59945d (1975) and Jap. Kokai No. 74 52,297, Chem. Absts. 82, 17934y (1975)). See also U.S. Pat. No. 3,381,019 which discloses the addition reaction between an alkenyl ether and a siloxane containing silanic hydrogen. Other patents mentioning --CH.sub.2 CH(CH.sub.3)CH.sub.2 -- groups between silicone and polyether blocks, or methallyloxy-- groups, include U.S. Pat. Nos. 3,233,968; 3,280,160; 3,507,815; 3,445,276; 3,663,468 (Example 5); 3,741,917; 3,796,676; 3,794,673 and 3,867,188. U.S. Pat. No. 3,652,629 to Imperial Chemical Industries discloses copolymers in which siloxane and polyether groups are joined by --CH.sub.2 CH(CH.sub.3)CH.sub.2 N--(CH.sub.2 CH.sub.3)CO-- linkages, prepared by hydrosilation of polyethers capped with a CH.sub.2 .dbd.C(CH.sub.3)CH.sub.2 N(CH.sub.2 CH.sub.3)CO-- group. However, none of these references disclose any advantage to using methallyl polyethers in preparing siloxane polyether copolymers either in higher yields or potency or with improved properties.
While it is known that other unsaturated polyethers containing nonisomerizable olefinic groups permit preparation of siloxane-polyether copolymers with low molar excesses of unsaturated polyether, these nonisomerzable olefinic groups are not amenable to incorporation in polyethers at both ends. For example, compounds containing norbornenyl groups (see U.S. Pat. No. 3,798,253, Ger. Offen. No. 2,301,789, Chem. Absts., 80, 109290x (1974)) or tertiary acetylenic groups (see Ger. Offen. No. 2,215,393, Chem. Absts., 78, 17121y (1973)), tertiary vinyl groups (see U.S. Pat. Nos. 3,957,843 and 4,059,605) can be used as polyether starters, but the same or equivalent compounds cannot be used as polyether capping groups. Accordingly, these disclosures are not helpful in preparing nonhydrolyzable (AB).sub.n block copolymers in the fashion taught by this invention. Other patents which disclose the non-isomerizable nature of norbornenyl groups, tertiary acetylenic groups and tertiary vinyl groups but which do not disclose siloxane-polyether block copolymers are U.S. Pat. Nos. 4,033,990; 3,842,112; 3,933,695 and 3,879,433. The disclosures of these patents provide no teachings, suggestions, or means which would enable the preparation of nonhydrolyzable (AB).sub.n block copolymers as taught by the present invention.
It is also known that linear siloxane polyether block copolymers having an (AB).sub.n structure can be prepared by reactions of dihydrosiloxanes with diallyl compounds. The methods make use of the .tbd.SiH/allyl group reaction. In such work, the dimethylsilicone contains only two .tbd.SiH groups located either terminally or internally in each molecule. For example, in U.S. Pat. No. 2,970,150 to D. L. Bailey (Example 16) MD'.sub.2 M (D'.dbd.OSiEtH--) and diallyl ether are reacted to form a polymer. In U.S. Pat. No. 3,836,560 to B. Prokai et al dihydropolysiloxanes with terminal .tbd.SiH groups have been reacted with diallyl polyethers to yield linear siloxane polyether block copolymers. The general reaction requires exact 1:1 stoichiometry for attainment of high molecular weights. (See U.S. Pat. No. 3,836,560, col. 10, lines 60-73 and note U.S. Pat. No. 3,280,160, Example 2). The general reaction is: ##STR3## The above-mentioned isomerization of allyl groups to propenyl groups destroys the 1:1 stoichiometry and acts as a termination reaction, limiting the value of n in the general reaction to about 10, and correspondingly placing severe limitations on the maximum molecular weight which can be attained.
Thus, the copolymers made from diallyl polyethers in U.S. Pat. No. 3,836,560 do not achieve the high molecular weights of their hydrolyzable analogues (see U.S. Pat. No. 3,792,073 to B. Prokai) and do not show the corresponding desirable foam performance properties of their hydrolyzable analogues.
Linear siloxane-polyether copolymers of high molecular weight have very useful properties as surfactants for the preparation of mechanically frothed urethane foam (U.S. Pat. No. 3,792,073) or of open-celled rigid urethane foam (U.S. Pat. No. 3,793,237). The desirable foam performance properties of these copolymers are derived from their high molecular weight. The utilization of such products has been somewhat limited by the fact that the only high molecular weight linear silicone-polyether block copolymers available in commercial quantities are hydrolyzable in nature, i.e., the siloxane and polyether groups are connected by .tbd.SiOC.tbd. bonds. These linkages are subject to hydrolysis by contained or atmospheric moisture, yielding silanol and alcohol groups and reducing the molecular weight of the product. The general hydrolysis reaction occurring is: ##STR4## Since performance of these products in dependent on their high molecular weight, they possess severe long term stability limitations under normal conditions, and cannot for example, be employed in premixed urethane foam formulations containing water or any other aqueous systems without breaking down.
In U.S. Pat. Nos. 3,716,517 and 3,716,518 siloxane copolymers are produced by the copolymerization of an oleophobic monomer and a hydrophilic monomer. The copolymers are applied to textiles to impart soil repellency and soil releasibility thereto. One type of hydrophilic monomer used contains two silyl groups (Formula IV) which are joined to a polyoxyalkylene unit by groups (R'" and R"") which may be isobutylene groups such as are derived from methallyl groups by reaction with hydrosiloxanes. However, there is no disclosure as to any advantage in using dimethallyl polyethers in preparing silicone-polyether copolymers in higher yields, higher molecular weights, or with improved properties for producing polyurethane foams. In fact, the process patents do not even involve a hydrosilation reaction between an organohydrosiloxane and a dimethallylpolyether. The polyethers in the processes of these two patents are reacted with hydrogen-containing silanes to form the hydrophilic monomers. These monomers and the oleophobic monomers are then mixed and subjected to a hydrolysis reaction to form the siloxane copolymers. In addition, the copolymers obtained contain substituents on the silicon atoms of the oleophobic portion which require a divalent bridging group (Z) linked at one end to a perfluoroalkyl group and at the other end to a --(CH.sub.2).sub.b group.
It is shown hereinbelow that the use of organic ethers or polyethers having two CH.sub.2 .dbd.C(R)CH.sub.2 -- end groups per molecule (wherein R is a monovalent hydrocarbon, most preferably methyl), as compared to diallyl ethers or polyethers results in the preparation of improved siloxane-ether copolymers having higher degrees of polymerization and higher molecular weights and low or substantially no silicon-bonded hydrogen therein, unexpectedly due to no, or only slight, isomerization of the CH.sub.2 .dbd.C(R)CH.sub.2 -- end groups to unreactive species during hydrosilation. It is also shown that the use of linear polyethers having two said CH.sub.2 .dbd.C(R)CH.sub.2 -- end groups in reactions with linear dihydrosiloxanes in the presence of a neutral platinum catalyst results in the preparation of higher molecular weight nonhydrolyzable linear siloxane-polyether block copolymers than are attainable with diallyl polyethers. It will also be a purpose of this disclosure to teach that such copolymers, which are novel compositions of matter, can be made with molecular weights and foam performance properties equivalent to the hydrolyzable, commercial products disclosed in U.S. Pat. No. 3,792,073, and that their hydrolytic stability is much greater than the commercial products disclosed in U.S. Pat. No. 3,792,073.
The 1968 Russian article by K. A. Andrianov et al, IAN SSSR 351, entitled "Reaction of 1,3-Dihydromethyldisilazanes and 1,3-Dihydrotetramethyl-disiloxane With Allylamines" discloses the production of higher molecular weight copolymers from 1,3-dihydrotetramethyldisiloxane and ethyldiallylamine in the presence of platinum on carbon catalyst as compared to the molecular weight of the copolymers made from the same reactants in the presence of a chloroplatinic acid hexahydrate catalyst; but it fails to disclose block copolymers made from ethers or polyethers having two hydrocarballyl groups.